The discussion below is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.
An automated directory assistance (DA) system is typically a spoken dialog system that provides a caller with the phone number and/or address of a desired business, government or residential listing. The DA system can be used to complement or replace the traditional human operated 411 services in order to cut cost.
A typical DA system includes two components, a speech recognizer and a search module. The speech recognizer receives a user's utterance and transforms it into text form. The text then serves as the basis for a query that is used by the search module in order to find the desired listing in a database of listings.
Due to errors made by the speech recognizer and the search module, the chance of finding the desired listing is typically well below 30% in most current DA systems if no special measure is taken to improve the search module. Speech recognition is nowhere near perfect. In fact, even using a domain specific language model (LM) trained with all listings for a given city, the speech recognizer may still have a word error rate (WER) of about 70% under some conditions. However, the search module often relies on exact matching of the query and the listing, and hence, is not robust to speech recognition errors.
Another source of errors is due to variations in users' references to listings. For example, the listing “Kung Ho Cuisine of China” is often referred to as “Kung Ho restaurant” or “Kung Ho Chinese restaurant.” Users' utterances often contain other information in addition to a business name, such as the spelling of the name or the street it is on.
Yet another source of errors is due to inconsistent text normalization for listings in the database. For example, 5 in “Big 5 Sporting Goods” is not normalized, while 9 in “K nine” is. So no matter whether inverse text normalization (ITN) is performed on ASR outputs or not, some queries will not match the listings on those terms.